A controller detects a rotor magnet temperature based on an actively detected back electromotive force (BEMF) voltage of the motor. The controller detects the BEMF voltage by commanding the injection of a direct-axis (d-axis) current into the motor while the motor is spinning but otherwise commanding no torque. The controller actively detects the BEMF voltage in that the controller purposely injects a known quantity of d-axis current at a chosen time during which the controller detects or is aware that the motor is commanding no torque. Using a quadrature-axis (q-axis) voltage equation, which describes the relationship between a voltage command, the current, the BEMF voltage, and reactance in the q-axis, the controller solves for the BEMF voltage with the voltage command, the current, and the q-axis reactance being known to the controller. The controller detects the rotor magnet temperature based on the BEMF voltage.